1. Field of the Invention
The present invention relates to solids inhibitors. The present invention particularly relates to solids inhibitors useful for applications in which naphthenic acid is present.
2. Description of the Prior Art
The forming of scale during the production of crude oil has long been a problem. The formation of scale can slow oil production rate and, in extreme circumstances, stop production completely. Some scale species are formed from the interaction of metals and inorganic anions. For example, the combination products of calcium cation with carbonate anion or phosphate anion will precipitate from the water in which the ions are carried to form scale deposits when the concentrations of these anions and cations exceed the solubility of the reaction product.
Another form of scale results from sulfides. The metal sulfide scale may be, for example, iron sulfide. Alternatively, the metal sulfide may be lead sulfide or zinc sulfide or a combination of iron or lead or zinc sulfides. The iron sulfide may be troilite (FeS) or pyrite (FeS2). Alternatively, the iron sulfide may be mackinawite (Fe9 S8) or phyrrhotite (Fe7S8).
Generally, the most common scale forming ions are calcium and barium, but sodium, carbonate, bicarbonate, chloride, sulfate, and strontium are also recognized as scaling species. The most common speciation of these combined scaling ions are: calcium carbonate (CaCO3), calcium sulfate (CaSO4), barium sulfate (BaSO4), and strontium sulfate (SrSO4). In addition, there are less common scale species, such as calcium fluoride (CaF2), iron sulfide (FexSx+1), zinc sulfide (ZnS), lead sulfide (PbS) and sodium chloride (NaCl).
In addition to the scaling species described above, crude oil will often include other materials which may form scale or scale like deposits down stream. For example, most crude oil will have agglomerative materials such as paraffins and asphaltenes. Most crude oil will also have clays and silica. All of these materials are known to contribute to problems with downstream equipment used to move and process crude oil.
It is widely known in the art that the processing of crude oil in its various fractions has led to damage of the iron-containing metal surfaces of associated apparatus due to naphthenic acid corrosion. It is also known that corrosion is not the only problem associated with the production, handling, and processing of crude oils having high levels of naphthenic acid. Naphthenic acids can also interact with metals, particularly calcium and sodium, to form solids and emulsions. These materials can form scale and block strainers and other equipment downstream from oil wells.
One method of treating naphthenic solids known to the art is to acidify production fluid as it leaves the well bore. It is known to use acetic acid and mineral acids for this process. One disadvantage of using acids at this stage of production is the cost of the acids, which may be required at high treatment levels. Some of these acids are dangerous and can pose safety hazards. It would be desirable in the art to mitigate or eliminate naphthenic acid solids formation downstream without resorting to the use of acetic or mineral acid treatment.